Mertzon is a city in and the county seat of Irion County, Texas, United States. The population was 839 at the 2000 census. It is part of the San Angelo, Texas Metropolitan Statistical Area.
Mertzon is located at 31°15′36″N 100°49′15″W / 31.26°N 100.82083°W / 31.26; -100.82083 (31.259951, -100.820759).
According to the United States Census Bureau, the city has a total area of 1.5 square miles (3.9 km²), all of it land.